Study to Evaluate the Pharmacokinetics, Safety, and Antiviral Activity of the Elvitegravir/Cobicistat/Emtricitabine/Tenofovir Alafenamide (E/C/F/TAF) Single Tablet Regimen (STR) in HIV-1 Infected Antiretroviral Treatment-Naive Adolescents and Virologically Suppressed Children

Key Inclusion Criteria:

• Cohort 1

• 12 years to < 18 years of age at baseline

• Weight greater than or equal to 35 kg (77 lbs)

• Plasma HIV-1 ribonucleic acid (RNA) levels of ≥ 1,000 copies/mL at screening (Roche COBAS TaqMan v2.0)

• Screening genotype report shows sensitivity to EVG, FTC and tenofovir (TFV)

• No prior use of any approved or experimental anti-HIV-1 drug for any length oftime

• Cohort 2

• 6 years to < 12 years of age at baseline

• Weight greater than or equal to 25 kg (55 lbs)

• Plasma HIV-1 RNA of < 50 copies/mL (or undetectable HIV-1 RNA level accordingto the local assay being used if the limit of detection is > 50 copies/mL) for ≥ 180 consecutive days (6 months) prior to screening on a stable antiretroviralregimen, without documented history of resistance to any component of E/C/F/TAFSTR.

• Cohort 3

• Age at baseline: ≥ 2 years old

• Weight at screening: ≥ 14 kg (31 lbs) to < 25 kg (55 lbs)

• Plasma HIV-1 RNA: < 50 copies/mL (or undetectable HIV-1 RNA level according tothe local assay being used if the limit of detection is > 50 copies/mL) for ≥ 180 consecutive days (6 months) prior to screening on a stable antiretroviralregimen, without prior history of resistance to any component of E/C/F/TAF STR

Key Exclusion Criteria:

• Hepatitis B or hepatitis C virus infection

• Evidence of active pulmonary or extra-pulmonary tuberculosis disease within 3 monthsof the screening visit.

• Individuals experiencing decompensated cirrhosis

• Pregnant or lactating females

Note: Other protocol defined Inclusion/Exclusion criteria may apply.